The public switched telephone network (PSTN) has evolved into an efficient real-time, multi-media communication session tool wherein users can pick up any one of nearly one billion telephones and dial any one of nearly one billion endpoints. Several developments have enabled this automated network, such as numbering plans, distributed electronic switching and routing, and networked signaling systems.
Numbering plans have developed over the years under the auspices of local, regional, and national authorities. Currently, based on an ITU-T standard called E.164, these numbering plans provide a generally hierarchical plan that can be used to route calls. The following provides an example of the North American numbering plan (NANP) hierarchy. For telephone number 1-978-933-6166: 1 indicates that the number is part of the NANP; 978 indicates that it is an area code in Massachusetts; 933 indicates that it is an exchange associated with Woburn, Mass.; and 6166 indicates that it is the number assigned to Acme Packet, located on 130 New Boston Street.
In a related manner, every telephone number in the world can be broken down into similar components, and a geographic determination can be made as to which network element (e.g., telephone switch) can terminate the communication. In recent years, portable number technology has been implemented to allow companies to make their numbers mobile in instances where they, for example, moved or relocated. Initially, this technology was directed toward toll-free numbers (e.g., 1-800-FLOWERS™) to permit the owner to change long distance carriers. In the development of portable number technology, the 800 exchange was recognized as a toll-free exchange and translated into a “real” network number that adhered to the fixed hierarchy at a database (i.e., service control point (SCP)). The process of resolving an 800 or toll-free number into a real number (i.e., shadow address) is known.
More recently, there have been further developments to make local numbers portable. The technology is similar to the toll-free technology discussed herein above in that an exchange is declared portable and a database (i.e., SCP) is used to get the location of the “real” address. The location returned is actually the telephone number of a terminating switch. The call is then placed to this phantom number on a signaling system #7 (SS7) network, with the real number carried passively as a separate information element to the endpoint in an initial address message (IAM). Once again, the number used to route the call was a real number that adhered to the fixed hierarchy. This mechanism for local number portability (LNP) is also known.
In wireless networks, a home location register (HLR) and visitor location register (VLR) mechanism is used. It should be noted that within wireless networks a telephone periodically registers on the networks with which it is capable of communicating. This registration informs the network of the location of the telephone so that calls can be appropriately directed to the user. To route calls to telephones that are within a local system (i.e., non-roaming), the equipment is capable of routing the call to/from a correct base station. To route calls between systems, a phantom number is allocated and a new call is directed to the new system, which then connects the telephone to a new endpoint. Within the wireless networks, the allocated phantom number is used to adhere to the established hierarchy.
Unfortunately, the PSTN is not currently capable of routing an actual communication session on anything other than an address that conforms to the hierarchy present in the PSTN since telephone numbers and their parts are used to discover a path to an endpoint of the communication. Portability mechanisms use a phantom or shadow number to direct the communication through the network.
Similar to the manner in which the PSTN is based on a hierarchy, the Internet is based on an Internet Protocol (IP). IP messages are routed or forwarded from one link to the next (i.e., from a source of the data flow to a destination of the data flow). Each IP packet contains an IP address, which, in Internet protocol version 4 (IPv4), has 32 bits. Each IP address also has a certain number of bits dedicated to a network portion and a certain number of bits dedicated to a host portion.
IP routers are used to take a packet from one network (or link) and place it onto another network (or link). Tables are located within IP routers that contain information or criteria used to determine a best way to route a packet. An example of this information may be the state of network links and programmed distance indications. Unfortunately, IP routers typically route packets by destination IP address, which does not assist in finding a proper route for transportation. There are some exceptions to this routing system, however. By using intelligent devices on both sides of a network domain, it is possible to allocate a temporary address to route a packet through a network and restore the original address on the far side of the network, when the packet leaves the network. This is the basis for many current virtual private network (VPN) products and is understood in the art.
Another exception to the routing system includes multi-protocol label switching (MPLS). MPLS is based on a technology developed by Cisco Systems, Inc. of San Jose, Calif. called tag switching. This method of routing IP packets allows a destination IP address to potentially be separated from the route that the packet actually takes through a network. One of the best uses of MPLS is to create a VPN or virtual leased lines (VLL). The MPLS tags can effectively encapsulate the routing of data packets through a network.
In summary, it is concluded that data networks base all real forwarding of IP packets on IP destinations. IP destinations, in turn, are associated with network topology and, like the telephone network, are used to deliver packets. MPLS tags and paths can provide override forwarding for IP packets based on a set of rules that is tied to the IP address portion used for routing, such as, for example, a forward equivalence class (FEC).
Distributed electronic switching and routing is important to making networks scale to required sizes. Distributed electronic switching and routing equipment need to have a defined role in a communication session. Networks simply would not scale if every endpoint had to manage a connection to every other endpoint. The distribution of control into a hierarchical scheme further emphasizes difficulty in changing underlying addressing.
To ensure that the network elements (e.g., switches in the telephone network, routers in the data network) can perform their associated tasks, they must know the status of adjacent communication links and available routes; signaling systems are used to provide this information. In telephone networks, signaling systems used are either SS7 or are equivalent to SS7. The signaling system provides information about individual links, link sets, routes, etc. In data networks, protocols such as border gateway protocol (BGP), interior gateway protocol (IGP), open shortest path first (OSPF), etc., are used to determine link states and routes.
In the telephone networks, the signaling system is also used to establish an end-to-end path (i.e., ISDN User Part (ISUP)) through the network. Unfortunately, in IP networks, there is no end-to-end path allocation. Instead, to engage in a communication session, there must be a system to associate endpoints with names or purposes.
Today's telephone networks use yellow pages, white pages, 411 directory systems, and other directory-like services to help users of the network find destinations. As businesses change telephone numbers or people move, the directories are updated. Additionally, most telephone networks will either forward calls or inform callers that the old user of an address has changed to a new address. Similarly, today's data networks use online directories to help users find other Internet users, but these directories are insufficient for many reasons. These reasons include, but are not limited to, the poor quality of information since most of the directories are built up from electronic-mail (e-mail) servers, the directory information is not maintained as part of a billing process, which leads to stale entries in most e-mail systems, and not all e-mail systems provide data to the directory providers.
In addition, Internet directories do not include a geographic location since geographic locations are not part of Internet domain addresses, unless the directory entry is entered manually. When trying to locate a user on a telephone network, the search can be narrowed if the city or town is known, but this type of search is not as easy in Internet directories. Uniform resource locators (URLs) typically define endpoints or locations on the Internet. A user name followed by a domain name is the current method to address users, wherein the domain name is owned by an entity that allows the user to employ it.
There are currently no known universal registries on the Internet. A universal registry with the domain name E164.com has been proposed by NetNumber.com, Inc. of Lowell, Mass. This universal registry development is based on a proposal by NueStar, Inc., which is now responsible for administering the NANP. This proposal calls for using the current domain name service (DNS) and formatting the numbers into URLs in a way that can be resolved using DNS servers. In this manner, each telephone number could be registered into a DNS server and distributed to all other DNS servers. The tail end of a DNS query could be a resource record, which points to a lightweight directory access protocol (LDAP) directory server.
The suggestion from the ITU to use Universal Portable Telephone (UPT) numbers for IP endpoints to avoid overlapping traditional wired telephone numbers is valid and would allow for addressable IP endpoints. It is possible to combine the above two proposals to enable Internet calling to and from the PSTN. Unfortunately, there are several limitations to this technology. These limitations include: DNS distribution and replication has significant latency; DNS address resolution can be slow; DNS servers may not be capable of handling the number of projected addresses; DNS servers are incapable of managing duplicate entries (except through round robin techniques); DNS employs parallel update mechanisms, which may result in unintentional duplicate entries; private network addresses or addressing gateways may result in duplicate entries or matches; no policy exists to handle the management of the resources requested; and, no solution exists to handle the number overlap between the PSTN and the data networks.
Due to most current telecommunication endpoints receiving service through a PSTN-based system, a gateway is used to facilitate a media flow between a packet data network and a PSTN. Gateways are installed at edges between data networks and voice networks, wherein the gateways are used to convert media (and signaling) to ensure communication. There are several strategies for routing calls received by gateways to other gateways described in the art. Two of these strategies are full mesh routing and hierarchical routing. Full mesh routing is the standard method described in most of the softswitching architectures. Session initiation protocol (SIP) is the inter-softswitch signaling system because it supports an anywhere-to-anywhere signaling model. In this model, all softswitches have a virtual connection to all other softswitches for completing calls. Routing tables are instantiated that can be used to direct traffic to a softswitch based on policy provided by the softswitch maker.
Unfortunately, when running a network that consists of many softswitches, the owner of the network has many different points of policy management that need to be maintained to create a full mesh. Such policy management issues include assuring that each softswitch “knows the IP address of each other softswitch and what telephone numbers or PSTN to which they connect.” When running softswitches from multiple vendors, further management issues arise. The management issues are then more complicated due to the fact that the equipment may be managed through different interfaces.
When the number of softswitches deployed grows large, the sharing of different routes is likely. In the full mesh routing arrangement, the routing of calls may be difficult since several different egress softswitches may be full or not functioning For example, if a carrier has 30 softswitches that can handle national long distance, and the network is running at about 50% full, then each originating softswitch will likely have to try an average of 15 separate softswitches before finding one with a non-blocked route. This search effort can be greatly reduced if a pure random distribution is implemented, however, it is assumed that some routes would be preferred over others due to cost or quality, thereby exacerbating the problem.
Certain simple gateways, such as, but not limited to, the Cisco AS5300, can forward SIP-based call requests to a SIP proxy server. Unfortunately, these gateways have low densities and frequently lack the sophistication of softswitches in setting up routing policies. These routers, therefore, cannot be interconnected to create networks without a softswitch controller.
In hierarchical routing, networks are segmented into different layers. The layers are interconnected into a pyramid to enable anywhere-to-anywhere routing. This method is the basis of the current PSTN. The hierarchical routing method uses a tiered model wherein the number of tiers in the hierarchy depends on the size of the network. The Internet today does not conform to a hierarchy. In fact, much of the Internet could be described as a full mesh, with many possible routes going from one place to another. One of the principal design goals of BGP is to avoid multiple circuitous routes, which indicate just how many different interconnections exist.
The hierarchical approach to networks was fairly standard in the PSTN, based on the local, national long distance, and international telephone networks; the business and political boundaries helped enforce this hierarchical model. Initial deployments of Voice over Internet Protocol (VoIP) that were based on the standard H.323 protocol drifted towards a hierarchical model when deployed en-mass.
Unfortunately, the hierarchical model can be complex when trying to apply it to today's peering environment. While the higher levels of the hierarchy are owned by some entity, from a business or political environment, it is hard to imagine how ownership and peering issues can be resolved since the data networks do not adhere to a hierarchy. Because the data network owners are competing for the same business, it is unlikely that peering arrangements, which are not mutually beneficial, can be established. The hierarchical model also creates single points of failure that can lead to larger ripple effects. The public data network PDN has evolved with no single points of failure, and largely subscribes to a distributed peer arrangement. Given this, single softswitches, which could affect large pieces of a network, are ill advised.
The hierarchical model also uses careful route configuration at every point in the hierarchy (i.e., no two softswitches can have the same configuration and no two softswitches can predict the route that a particular communication will traverse). A hierarchical routing system therefore uses a distributed route plan in an incredibly coordinated manner. Finally, the hierarchical model has vendors adhere to similar signaling systems to ensure proper routing, end-to-end. For example, to enable proper routing, each softswitch would have to share information about circuit availability to ensure proper route-around functionality as the network becomes full. Since there are currently no standards for accomplishing this, vendors have been building proprietary methods; and these proprietary methods may not interoperate correctly.